MK-910, a new drug chemically related to metronidazole, demonstrated marked amebicidal activity in both in vitro and in vivo tests, with a wide margin of safety. We carried out a clinical study of the effectiveness of the drug in 30 patients with hepatic and intestinal amebiasis. Two dosage schedules, 0.5 mg and 1.0 mg of the drug per kg of body weight per day, given orally, proved to be effective for the treatment of both forms of amebiasis. With the exception of transient paresthesia in one patient, there were no side effects or evidence of toxicity. Further clinical trials are required to evaluate more precisely the therapeutic efficacy of the drug.